You might check Tools > Options > Advanced and make sure that Automation
Events are turned on. If not, turn them on and then reload your file.
Another possibility is to try starting a new timeline drawing from the blank
template. Then copy/paste your timeline into the drawing.
Beyond that you can post a version of your file to see if someone can find a
more specific problem.
--
Mark Nelson
Microsoft Corporation
This posting is provided "AS IS" with no warranties, and confers no rights.